Electrorefining of nickel



Feb. 12, 1946.

L. S. RENZONI ELECTRO REFINING OF NI CKEL Filed Jan. 15, 1943 i ia".

HNOLY TE CEMENT/7770A THNK No.

CEMENT CU, /w' 7-/0Z CEMENTHT/ON Cu eo-soZ CEMENITH T/ON CEME/VTHT/ONTHN/r No.4-

IV/ PC WD ER DORR TEN/1 9 Sheets-Sheet 5 CEME/V 7' 6'0 AND U/VREHC TED/v/' POWDER CEMENT/ T/ON TEN/f No.6

CEMEN 7-H T/ON TH/wr No. 7

CEMENT 60 FROM TEN/1'8 N065? Fl; TRH TE F/L TER PRESS us .574 TEMP/55FLOU/SSRENZON/ INVENTOR.

HTTORNEY Feb. 12, 1946. L. s. RENZONI 2,394,874

' ELECTRO-REFINING 0F NICKEL Filed Jan. 15, 1943 a Sheets-Sheet 9lNl/E'N TOR 4 OU/S 6.RENZO/V/ HTTORNEY sulfaltlebt biite, The prbqqss asusually on? I it4nvQ Y Jt ilsel ia e lha i iz phragm' separatingthe,anode cpmpgi tn ent min a s niq" ea andiqopne i1-111 not. n .10 npracticgl inejal'iogi for the xcon tinuong :rqmoiaL 91 them-rare .extenis i fl ulnf nera f an non .imnu i iei l rsti. for 911.; ligri ibgdrkp yid u me ze c yt whi h ntrpduqq lfiioa lle thqd QQWWE WP -SM m wcells atsu i itbi 0 his *pro ded y lead, Y1 a. reducing agent followedby addition or acid H carried out on an industrial scale. It has been 56in whichiron, lead, arsenic and*cobalt are remov eci by bxidiitipn n v"precipitationisrior wine QW- QlfJFQP-PI ic ema i i The presentinvention also contemplates a proqes by 'whici 'piiimary slimescontaining irjon,

senic; coppei and. cobalt iare it'reatedzwith for flcation of the impureanolyte and for the electro-deposition of cathode nickel orelectro-nickel from purified electrolyte in accordance with theprinciples of the present invention;

Fig. 8 is a photomicrograph taken at 500 magnifications ofelectro-nickel produced in an allsulfate ion bath at 12 amperes persquare foot; and

Fig. 9 is a. photomicrograph taken at 500 magnifications ofelectro-nickel produced in a sulfate-chloride electrolyte at 16 amperesper square foot.

Briefly stated, the electro-refining of nickel involves the productionof impure nickel anodes which are cast in any suitable manner andgenerally have a nickel content of about 90% to about 96%. Dependentupon the source of the nickel from which the impure nickel anodes areproduced, such anodes will contain greater or lesser amounts of theimpurities present in the ore. Thus, for example, in one industrialoperation, the impure nickel anodes contain about 94% to about 96% ofnickel, about 2.5% to about 3.5% of copper, about 0.7% to about 0.9% ofcobalt, about 0.5% to about 1.0% of iron, about 0.002% to about 0.004%of lead, about 0.05% to about 0.07% of arsenic and about 0.5% to about0.8% of sulfur.

The electro-refining of nickel involves solution of the metallicconstituents of the impure anode in the anolyte followed by purificationof the anolyte to remove iron, copper, cobalt, lead, arsenic, etc. toobtain a purified electrolyte from which electro-nickel can be produced.

Electrolytic nickel produced in the all-sulfate electrolyte has thefollowing composition:

The general features of the electrolytic cell preferably employed inconjunction with the Hybinette bag are described more or less in detail,together with the process employed in conjunction therewith, in theHybinette U. S. Patent No. 805,969. In the prior art all-sulfateprocess, the electro-refining of nickel is generally and preferablycarried out employing Hybinette bags. As those skilled in the art know,the Hybinette bag generally comprises a wooden frame of spruce or thelike covered with a canvas of such weight that a slight hydrostaticpressure maintained on the cathode side of the canvas substantiallypreventsthe migration of copper, cobalt, nickel, iron and similarcations from the impure electrolyte through the canvas diaphragm intothe purified electrolyte present as a catholyte in the cathodecompartment of the cell.

As clearly set forth in U. S. Patent No. 805,969, a hydrostatic pressureis maintained in the cathode compartment and impure anolyte withdrawnfrom the anode compartment continuously. The impure anolyte is firstsubjected to purification to remove copper and. in the all-sulfate ionelectrolyte, the copper is removed by cementation through addition ofnickel, preferably in the form of freshly reduced nickel powder, beforethe iron, lead and arsenic are removed. After the copper has beenremoved by cementation, the iron, lead and arsenic are then removed.When desired,

the cobalt is removed in the all-sulfate ion. electrolyte by theaddition of nickel, preferably in the form of an oxide or hydrated oxideprepared outside the electrolyte system by the action of a strongoxidizing agent upon nickellous hydrate. whereby the nickel goes intosolution and the cobalt is precipitated. This, however, is a difiicultand costly operation. In order to derive the advantages of lower tankvoltage, higher anode efliciency, lower steam consumption, betterpurification of impure anolyte, the production of a more highly purifiedelectro-nlckel, and other advantages of the present invention, it wasfound that the sequence of steps for the purification of the impureanolyte which had provided satis factory results when employed inconjunction with the all-sulfate-ion electrolyte was inefiective whenemployed in conjunction with the novel electrolyte of the presentinvention containing chloride ions equivalent to up to about 50 grams ofsodium chloride per liter.

In the operation of the all-sulfate process, anode efliciency is lowerthan cathode efiiciency which results in anolyte flowing from theplating tanks at pH 3.0 to pH 3.2. This value is too low for ironhydrolysis and must be raised to a minimum of pH 5.0 before attemptingiron precipitation. The pH rise is brought about by carrying out coppercementation before iron hydrolysis. The nickel powder functions incementing copper and in neutralizing excess acid. Thus, in one operationusing anodes containing 2.65% copper. the cementation of pounds ofcopper requires the dissolution of 1'73 pounds of reduced nickel powder.Of this amount, 92 pounds are required for cementing copper and 81pounds for neutralizing acid. In the sulfate-chloride process, anodeefiiciency is practically equal to cathode efficiency and anolyte pH is4.6. This allows for the removal of iron in the presence of cupric ions.During copper cementation the amount of excess acid present is small.Thus, in the operation usin anodes containing 2.65% copper, thecementation of 100 pounds of copper requires 133 pounds of nickelpowder, of which 41 pounds are consumed for acid neutralization. Theoperation of the sulfate-chloride process, therefore, shows a clearsavingin nickel powder consumed for copper cementation.

In order that those skilled in the art may have a clearer understandingof the present invention, the process will first be described inconjunction with the simplified flow sheets, Figures 1 to 6, and thenthe process will be described in conjunction with the drawings, Figs. 7and 7a.

The refining of nickel-containing material by electro-deposition ofnickel from a purified electrolyte involves the use of a number ofelectrolytic cells employing a diaphragm to separate impure anolyte fromthe catholyte. The number of cells required is, of course, dependentupon the amount of nickel to be electro-deposited in a unit of time,most of the cells being operated with a soluble anode while a few of thecells are operated employing insoluble anodes. The soluble anodes areobtained by casting or otherwise forming from impure metallic materialcontaining a relatively high percentage of nickel, but also containingso much of the impurities, copper, iron. cobalt. lead, arsenic andsulfur, that the impure anodes are not acceptable, per se. to the tradeas pure nickel. The impure anodes are immersed in the anode compartmentof the diaphragm cell in contact with lean anolyte obtained fromprevious operations, 1. e., catholyte, the nickel content of Thus, aniron slime, which may be'called secondary iron slime, is formed and isseparated from the fluids containing nickel, cobalt and copper in theform of soluble salts. The secondary iron slimes contain about 40% ironand small amounts of copper, cobalt, and nickel which may be treated inany suitable manner for the recovery of copper, cobalt and nickeltherein contained. The fluid portion containing the nickel, cobalt andcoppe as sulfates, preferably, is treated with nickel powder at a pH ofabout 5.2 to precipitate the copper as cement-copper and thecement-copper is removed in any suitable manner such as, for example, bya filter press. The fluid portion containing the nickel and cobalt assulfates is treated with an alkaline oxidizing agent to preferentiallyoxidize and hydrolyze the cobalt. Preferably, an alkaline solution ofsodium hypochlorite is employed as the oxidizing and precipitatingagent. The cobalt is precipitated as a hydrated oxide or hydroxidecontaining from 53 to 55% cobalt, 2 to 4% nickel, and traces of copperand iron. The precipitate is allowed to settle and the supernatantnickel solution, now containing onlyapproximately 0.2 gram per litercobalt is removed by decantation. The nickel values are recovered fromthis solution by precipitation as basic nickel carbonate which is thencollected in a filter press, washed, resuspended in water and added tooxidation tank No. 3 of the nickel electrolyte purification system tosupply a portion of the alkali required for cobalt hydrolysis. The firstcobalt precipitate is resuspended in water and redissolved by theaddition of sulfur dioxide and sulfuric acid. Th resulting solution,containing approximately 30 grams per liter cobalt, and 1 to 2 grams perliter nickel is again treated with an alkaline sodium hypochloritesolution and the cobalt is again precipitated. The second cobaltprecipitate contains from 55 to 57% cobalt, from 0.4 to 0.6% nickel andtraces of copper and iron. The fluid portion from the second cobaltprecipitation contains approximately 0.5 gram per liter nickel andapproximately 0.2 gram per liter cobalt and is used for washing thefirst cobalt precipitate; It is believed that the reduction of the ironfrom the ferric state to the ferrous state and the oxidation ofthe'reduced iron to the ferric state fol-- lowed by hydrolysis andprecipitation as ferric hydroxide is illustrated by the followingequation:

2Fe(OH)3+2Co(OH)3+2Ni(OH)3+ In Fig. 4 there is provided in a more orless diagrammatic manner a simplified flow sheet illustrative of theremoval of arsenic and lead. After the oxidation and precipitation ofthe iron has been completed, chlorine is introduced into the impureelectrolyte and the arsenic, lead and cobalt oxidized to the higherstates of oxidation. Instead of the chlorine, other oxidizing agents,such as hydrogen peroxide, persulfates, and the like. could be employed,but it is preferred to use chlorine in view of the fact that an amplesupply is available at the insoluble anode of the electrorefining cells.The arsenic, lead, and, if desired, cobalt are oxidized. The arsenic andlead precipitate, together with the iron, may be removed as primary ironslimes. When it is desirable to remove the cobalt at the same time asthe iron,

arsenic and lead are removed, it is necessary to maintain the. solutionat a pH of about 4.0 to about 5.0 and preferably at a. pH of about 4.5and to augment the chlorine produced at the insoluble anodes withchlorine from an outside source. In order to establish and maintain thedesirable pH for precipitation of cobalt, an alkali is added, preferablybasic nickel carbonate, to the impure electrolyte in sufilcient quantityto maintain a pH between the aforesaid limits.

The flow sheet of Fig. 5 is illustrative in a more or less diagrammaticmanner in a simplified way of the removal of copper from the partiallypurified electrolyte by cementation. The partially purified anolyte isintroduced into the first cementation tank into which likewise areintroduced the solids from the settler or Dorr tank. The contents of thefirst cementation tank then pass to the second cementation tank fromwhich the cement-copper is removed. This cementcopper contains about tocopper and about 7% to 10% nickel and is further treated for theseparation and recovery of the values contained therein. The impureelectrolyte passes from cementation tank 2 (corresponding to tank I ofFig. '7) to cementation tank 3 (corresponding to tank l5 of Fig. 7)where nickel is added at intervals, preferably, and in amountssufllcient to maintain the copper content of the overflow from thesettling tank (or Dorr tank l8 as shown in Fig. '7) below a particularvalue of about 0.01 to about 0.02 gram per liter. Cement-coppercontaining some nickel is likewise introduced into cementation tank No.3 (corresponding to tank l5 of Fig, 7). 'The precipitated copper and thepartially purified electrolyte then pass to two additional coppercementation tanks to allow sufficient time for the reaction, and thenceto a settling tank or Dorr tank where the solids are removed andconveyed to the first cementation tank and the overflow or solution ofpartially purified electrolyte passes to cementation tank No. 6(corresponding to tank IQ of Fig. 7) where the nickel powder necessaryto remove substantially all of the residual copper is added. To providetime for the reaction to reach completion, the contents of cementationtank No. 6 (corresponding to tank [9 of Fig. '7) are conveyed tocementation tank No. '7 (corresponding to tank 20 of Fig. '7) and thento a suitable means for removing cement-copper from the solution, suchas fllter press 22 (Fig. 7) The filter press has been found to besatisfactory for this purpose. The filter cake comprises thecement-copper and unused nickel powder and is returned to cementationtank No. 3. When the cobalt has been removed with the iron, the filtratecontains about 0.001 gram to about 0.01 gram, preferably about 0.005gram per liter of cobalt and is of sufficient purity to be electrolyzedin the electro-refining cells. When the cobalt has not been removed inthe iron removal unit, the filtrate is passed to the cobalt removalsystem. The reaction by which the copper is cemented out of solution isbelieved to be illustrated by the following equation.

CllC12+Ni NiC1z+Cu pH 4.2 to 5.4 Temperature F During the cementation ofthe copper, it is preferable to maintain the temperature of theelectrolyte at about 135 F. and to allow the pH to rise from about 4.2to about 5.4. However, a temperature between about 120 F. and about F.

and a pH within the range of about 4.0 to about 5.5 are alsosatisfactory.

In the event that the removal of iron, arsenic and lead is carried outunder such conditions that the cobalt is not precipitated, it isnecessary to remove the cobalt after the iron, arsenic, lead and copperhave been removed from the impure anolyte. Such an anolyte may be termedpartially purified electrolyte. The removal of cobalt is illustrated ina simplified and more or less diagrammatic manner in Fig. 6. Thepartially purified electrolyte containing about 0.0002 to about 0.0005gram per liter of copper and about 0.12 gram per liter to about 0.15gramper liter of cobalt is conveyed to a reaction tank into whichmolecular chlorine and nickel carbonate are introduced in sufficientquantities to precipitate cobalt to yield a purified electrolytecontaining a residual concentration of 0.001 gram per liter to 0.01 gramper liter cobalt. The cobalt precipitates as an oxide or hydrated oxideat a pH of about 4.5 to about 5.0. The suspension istreated to removethe cobalt precipitate in any suitable manner and preferably with afilter press to obtain a cobalt precipitate containing about 18% toabout 20% cobalt, about 25% to about 30% nickel, about 0.005% to about0.01% iron, which is then treated preferably in accordance with theprocess illustrated in Fig. 3 for the recovery of the cobalt. Thefiltrate which is now the purified electrolyte for direct introductioninto the cathode compartments of the electro-refining cells containsabout 0.001 to about 0.01 gram per liter of cobalt, about 0.0002 gramper liter to about 0.0005 gram per liter of copper, about 0.0001gram perliter of arsenic, about 0.0001 gram per liter of lead, and about 0.0001gram per liter of iron. It is believed that the reaction to precipitatecobalt in the aforesaid described manneris illustrated by the followingequation:

The impure anolyte is removed from the anode compartments I (Fig. 7) andtransferred by means of conduit 2 to a holding tank 3. The impureanolyte as withdrawn from the anode compartments has a temperature ofabout 130 F. to about 140 F., a pH of the order of pH 4.6 and containsabout 0.25 gram per liter to about 0.35 gram per liter of copper, about007 gram per liter to about 0.10 gram per liter of iron, about 0.0002gram per liter to about 0.0004 gram per liter of lead, about 0.004 gramper liter to about 0.006 gram per liter of arsenic, and about 0.12 gramper liter to about 0.15 gram per liter of cobalt. The impure electrolytein holding tank 3 is then conveyed in any suitable manner, for exampleby means of pump 4 and conduit 5, to the unit for removal of iron,arsenic and lead which comprises four or more containers, such as tanks6, I, 8 and 9, connected in series. The contents of tanks 6, l and 9 areagitated, preferably by air introduced therein by means of conduit 28.The removal of iron, arsenic and lead is based upon the oxidation of theiron, arsenic and lead.

and the precipitation of these materials as oxides or hydrated oxides orhydroxides or as insoluble iron and lead compounds of arsenic. In orderto precipitate the arsenic and lead, it was found necessary to introducean oxidizing agent, such as hydrogen peroxide, persulfates, sulfurdioxide and air or chlorine into the reaction mixture after the iron hadbeen oxidized and precipitated.

' tates as the hydroxide.

This is quite contrary to usual practice when purifying an impure allsulfate-ion anolyte.

In-the impure anolyte, a portion of the copper is present as cupricions. The iron is oxidized at the expense of the cupric ions and thecupric ions reoxidized by air passed into theoxidation tanks. Theoxidized iron then hydrolyzes and precipi- The pH change during theoxidation of the iron and the precipitation thereof is very slight,being equivalent to a drop from pH 4.6 to pH 4.5. It would appear thatthe successful oxidation of the iron and precipitation thereof isdependent upon the ratio of cuprous the trivalent to the pentavalentstage and for the oxidation of lead from the bivalent to the tetravalentstage. Preferably, the chlorine is obtained from the anode compartmentsof the e1ectrorefining cells 84 having insoluble anodes. At the sametime, more or less of the cobalt present in the impure anolyte islikewise oxidized and under proper conditions can be removed, togetherwith the iron, lead, arsenic and some copper. However, when desirable,the removal of iron, lead and arsenic can be so controlled as tosubstantially eliminate the removal of cobalt at this place in thepurification system and the cobalt can be removed at a later stage ingreater purity. The oxidation of the iron, lead and arsenic issubstantially completed in oxidation tankv 8 and,

oxidation tank 9 is only provided to insure the completion of thereaction. The arsenic content of the electrolyte is lowered from about0.005

' tank I 3.

gram per liter to about 0.0001 gram per liter after passage throughoxidizing tank 8. The iron, arsenic and lead precipitates, together withany cobalt and copper which are precipitated, are removed as primaryslimes in any suitable manner, preferably by any suitable mean H to a.filter press 12. The filter cake (primary iron slimes) is treated forthe recovery of cobalt as hereinafter described in conjunction withFigs. 3 and 7a, while the filtrate is further treated to remove copperand traces of cobalt.

Copper is removed by cementation after the removal of iron, lead andarsenic has been completed and is carried out in the copper cementationsystem as illustrated in a diagrammatic manner in Fig. '7 and in thesimplified flow-sheet Fig. 5. The copper cementation unit includes sevenor more cementation and holding tanks l3, l4, l5, l5, l1, l9 and 20 anda settler l8, such as a Dorr tank. The filtrate from the primary slimesseparation (accomplished in filter press 12) is introduced throughconduit 2| into cementation Freshly reduced nickel powder is introducedinto cementation tank l9 into which the overfiow of the settler or Dorrtank 18 is introduced. The eflluent from cementation tank 20 passes to afilter press 22 or other means of separating solids from liquids inwhich the cement copper, together with some nickel, is separated fromthe partially purified electrolyte. The

solids from this separation containing an appreciable amount of nickelare introduced into cementation tank l by suitable means 23. Additionalnickel powder, together with the filter cake from press 22 is likewiseintroduced into cementation tank l5 in amounts sufficient to maintainthe copper content of the overflow from the settler tank not greaterthan about 0.02 gram per liter. The solids settling out in the settleror Dorr tank are returned to the first cementation tank [3 of the systemby suitable means, such as pump 24 and conduit 25, and the cement copperis removed from cementation tank l4 in any suitable manner.

Dependent upon the conditions existing in the unit for the removal ofiron, arsenic and lead, the electrolyte flowing from the coppercementation system is more or less purified of cobalt. In the event thatsuiflcient cobalt has been removed in the iron, lead, arsenic system,the electrolyte is sufficiently purified to be introduced directly intothe cathode compartments 3| of the electrolytic cells by means ofconduit 26. On the other hand, if sufficient cobalt has not beenremoved, the electrolyte flowing from the copper cementation unit,filter press or the like 22, is transferred by means of conduit 21 totank 28 and treated with chlorine plus nickel carbonate ConstituentsGrams per liter From about 0.001 to about 0.01. From about 00002 toabout 0.0005. About 0.0001. About 0.0001.

About 0.0001.

It is preferred to maintain the electrolyte at a temperature betweenabout 130 F. and about 140 F. during purification andelectro-deposition. The pH of the catholyte during electrodeposition ispreferably maintained at about 4.0 to about 5.0.

It is desirable to recover the cobalt whether precipitated with theiron, arsenic and lead or removed separately. Furthermore, in view ofthe fact that an appreciable amount of nickel is precipitated with theiron, lead and arsenic of the primary slimes, it is desirable to furthertreat the primary slimes, whether they contain cobalt or not, to recoverthe nickel contained therein and to reintroduce the nickel so recoveredinto the electro-refining system.

In the event that the primary slimes contain cobalt in amounts greaterthan 5% to 6%, the treatment of the primary slimes differs from thetreatment to which the primary slimes are subjected when the primaryslimes contain less than 5% cobalt. When the primary slimes contain morethan 5% to 6% cobalt, the primary slimes from filter press l2 areintroduced into container 33 by suitable means such as conduit 34 andsuspended therein in water (Fig. 7a). Sulfur dioxide, or any othersuitable reducing agent is introduced and the reduction reaction isallowed to proceed until all of the nickel, cobalt and copper, and fromabout 5% to about 10% of the iron are reduced from the oxidized to thereduced states. When sulfur dioxide is used as the reducing agent, theend point of the reaction is reached when the pH value of the suspensionhas been reduced to pH 4.3 to pH 4.5. Any suitable acid, preferablysulfuric acid, is then introduced in an amount required to reduce the pHto 1.5 to 2.0 at which value the slime is completely dissolved; Duringthe reaction, the tem perature in container 33 rises from about F. toabout F. and no external heat is required. When the reaction iscompleted, the cobalt and nickel compounds and preferably a part of theiron and copper compounds of the primary slimes have been reduced andbrought into solution.

The solution of the values of the primary slimes is then transferred tocontainer 35 (Fig. 7a) by means of conduit 36. Further amounts ofprimary slimes are. introduced into container 35 by means of channel 31.The primary slimes have an oxidizing effect on ferrous and cuprous ionsand an acid neutralizing effect which may be expressed by the followingreactions:

The reaction is complete when the pH rises to pH 4.3 to 4.5. Theoxidation reaction is carried out at 180 F. By suitable control it ispossible to carry out the reaction to yield a solution of cobalt,nickel, and copper essentially free of iron, and to produce a secondaryiron slime containing about 1% to about 2% cobalt, about.2% to about 4%nickel, about 5% to about 7% copper and about 36% to about 40% iron,from 2.5% to 3.5% arsenic and about 0.2% to 0.3% lead.

The suspension of primary slimes in container 35 is transferred tofilter press 38 by any suitable means 39. The fluid portion of thesuspension of the primary cobalt-containing iron slimes after separationfrom the secondary iron slime by any suitable means, such as filter 38,is transferred to container 40 by suitable means 4| and treated withreduced nickel powder in container 40 at a temperature of about F. toabout F. and preferably at about 150 F. and at a pH of 4.5 to about 5.5,and preferably at about pH 5.2. Under these conditions, the coppercontained in the primary iron slimes and present in the fluid portion ascopper sulfate, or chloride, or both, is precipitated out ascement-copper by the addition of the nickel powder. The suspensioncontaining the cement-copper is then transferred by any suitable means42 to filter press or the like 43 and the cement-copper separated fromthe fluid portion containing nickel and cobalt as soluble nickel andcobalt sulfates and/or chlorides. The solution containing the nickel andcobalt as soluble salts is then transferred by suitable means 44 tocontainer 45, to which alkaline sodium hypochlorite is added. Thishypochlorite solution is made up preferably by chlorinating a soda ashsolution containing 3.89 pounds of soda ash per pound of chlorine added.Sufficient hypochlorite solution is added to container 45 so that thecobalt is precipitated as a hydratedcobaltic oxide. The residual cobaltcontent of the solution is reduced to 0.2 gram per liter cobalt by thismeans. For the precipitation of the cobalt, the temperature of thesolution should be maintained at about 80 F. to about 120 F., andpreferably at about 100 F. and the pH should be maintained within therange of about pH 1.8 to about pH 2.4 and preferably at about pH 2.3.The precipitated cobalt contains 53 to 55% cobalt and 2% to 4% nickelafter the initial separation from the nickel bearing solution. Theprecipitate 'formed in tank 45 is allowed to settle, the liquid portiondecanted, the precipitate washed once with water, resuspended withwater, and redissolved with sulfur dioxide plus sulfuric acid. Bysuitable control, a

solution free from sulfur dioxide at pH 2.0 is

obtained. The solution at this point contains approximately 30 grams perliter cobalt and 1 to 2 grams per liter nickel. The cobalt is againprecipitated by the action of alkaline sodium hypochlorite to yield aprecipitate containing 55% to 57% cobalt and-0.4% to 0.6% nickel, and asolution containing approximately 0.2 gram per liter cobalt andapproximately 1 gram per liter nickel. The precipitate is allowed tosettle, the fluid portion decanted or separated by any suitable means,and the precipitate washed twice by decantation and finally separatedfrom the wash water by means of filter press 46 into which thesuspension is introduced b suitable means 41. The fluid electrolyte,after the initial removal of cobalt to provide a nickel solutioncontaining not more than about 0.2 gram of cobalt per liter, is.

then transferred by means of channel 48 to tank 49 and treated with sodaash to precipitate the nickel as basic nickel carbonate. This suspensionis transferred by suitable means 50 to filter press or the like and thenickel carbonate separated. The precipitate is washed, re-emulsifiedwith water in tank 52 and transferred to oxidation tank 8 by means ofconduit 53 to assist in the precipitation of cobalt.

When the primary iron-slimes are substantially devoid of cobalt, thetreatment to which the primary iron slimes is subjected is somewhatdifferent from that to which primary iron slimes containing cobalt issubjected. This treatment of primary iron slimes substantially devoid ofcobalt will be discussed in conjunction with the unit for recovery ofnickel from primary iron slimes (Figs. 7 and 7a). The primary ironslimes substantially devoid of cobalt are transferred by means ofchannel 55 to container 56 (Fig. 7a). Anode slime wash water containingabout 3 grams per liter to about 5 grams per liter of chloride ion isintroduced into container 56 by means of conduit 51, When desired, anodeslime wash water can be added by suitable means 58 to the 4 suspensionof the primary iron slimes substantially devoid of cobalt in channel 55in addition to introducing the anode slime wash water into container 56.The suspension is then conveyed by means of conduit 59 to container 60where a temperature of about 170 F. to about 180 F. is maintainedtogether with a pH of about 2.0 to about 3.5. Anolyte, from the anodecompartments of the electro-refining cells having insoluble anodes, islikewise introduced into container 60 by means of conduit 6|. Theanolyte so introduced has a pH of about 1.3 to about 1.5 and containsabout 0.2 to about 0.4 gram per liter of molecular chlorine. Under theseconditions, the major portion of the nickel of the primary iron slimes,together with some arsenic, lead, iron and copper pass into solution.The suspension is conveyed, as by pump 62 and pipe 63, to filter press64, or any other suitable means, wherein the solids are separated fromthe fluid portion of the suspension. The fluid portion containingnickel, copper, some iron, arsenic and lead is conanodes, the preciousmetals, gold, silver and the metals of the platinum metal group remainon the corroded anodes as anode slimes. This anode slime is washed offthe residual portion of the soluble anodes 66 in tank 61, preferablywith impure electrolyte or anolyte in conduit 68, as illustrated inFigs. 7 and 7a (precious metals recovery unit) from which it flows intoslime sump 69. The suspension of anode slimes is then transferred bysuitable means such as pump 10 and pipe H to a holding tank 12 and.finally through channel 13 to a means 14 for separating the fluidportion from the solid portion. The fluid portion is returned to theanode slimes suspension sump 69 by means of conduit 15, while the solidportion is conveyed by suitable means I6 to a holding tank 11 where itis suspended in wash water at a temperature of about F. to about 160 F.,and preferably about F. The slimes are then transferred by suitablemeans 18 to a washing filter press 19 and washed therein until the washwater has a chlorine content not greater than about 0.002 gram perliter, and the washed slime a residual chlorine content of 0.1% to 0.2%.This washing operation is quite necessary for the efllcient recovery ofthe precious metals in the anode slimes. In the presence of smallamounts of chlorine a relatively large portion of the precious metals islost in later steps of the purification process. The thoroughly washedprimary slimes are then transferred directly to a calciner. The washedfilter cake is transferred directly to a calciner 80 by any suitablemeans 8I. The slimes'are roasted to reduce the sulfur content toapproximately 0.2% and to obtain oxides of the base metals and some ofthe platinum group metals. The resulting oxide is then charged into anelectric anode furnace 82 along with the proper percentage of coke, andthe metal is cast in regular anode moulds 83 to form secondary orprecious metal anodes. These are returned to the electro-refining cellsand are corroded in regular soluble anode cells set aside for thepurpose. To prevent loss of slime during corrosion, these anodes arewrapped in closely woven cotton duck. After essentially completecorrosion, the anode scrap, together with the adhering slime, istransferred to the precious metal concentrating plant where the slime iscarefully removed from the scrap and treated with acid for the removalof the base metals from gold and the metals of the platinum group. Thesecondary anode scrap is returned to the electric anode furnace 82 andreturns to the electrolytic nickel refinery as secondary anodes.

In carrying out the electro-refining of nickel in accordance with theaforedescribed process, it is essential that the pH ofelectro-deposition be not higher than about pH 5.0 and not lower thanabout pH 4.0. The amount of iron present in the impure anolyte should beequal to at least about 15 times the sum of the arsenic and lead presentin the impure anolyte. The copper present in the i'mpure anolyte shouldbe equal to about 3.0 to about 4.5 times the amount of iron present inthe impure electrolyte and it is desirable to maintain the ratio ofnickel to sodium in the electrolyte at not less than 1.50 to 1.00.However, the total sodium present should not exceed 30 grams per literequivalent to about '15 grams per liter of sodium chloride. In practiceit is preferred to maintain the sodium chloride content at about 50grams per liter. If it is desirable to increase the chloride ionconcentration, without further increasing the total sodium ionconcentration, it may be accomplished by the addition of calciumchloride to the sulfate-chloride electrolyte followed by filtration toremove the precipitated calcium sulfate. In this manner the chloride ionreplaces an equivalent amount of sulfate ion in the solution and thereis no increase in the total cation content of the solution. This schemeis used to advantage in changing from an all-sulfate nickel electrolytehaving a relatively large concentration of sodium sulfate tosulfate-chloride nickel electrolyte having a desirable maximum sodiumion concentration of 30 grams per liter. The chlorine necessary for theoxidation of the cobalt is about 2.5 to 3.5 times the theoreticalamount. The nickel required for copper cementation is about 1.4 to about1.5 times the theoretical amount. Nickel required for copper cementationfrom all-sulfate electrolyte is about 1.9 to about 2 times thetheoretical amount. The electrolyte preferably has the followingcomposition:

Constituents Grams per liter About 40 to about 60. About 27 to about 30.About 71 to about 120. About 10 to about 35. About 45 to about 50. Aboutto about 25.

The impure anolyte prior to treatment to provide purified electrolytehas the following composition:

Constituents Grams per liter About 40 to about 60. About 27 to about 30.About 71 to about 120. About 10 to about 35. About 45 to about 50. About15 to about 25. About 0.12 to about 0.15. About 0.07 to about 0.10.About 0.25 to about 0.45.

About 0.004 to about 0.006.

About 0.0002 to about 0.0004.

The purified electrolyte has the following composition:

Constituents Grams per liter The pH of the anolyte in the anodecompartments of the cells having soluble anodes should be maintainedbetween a pH of about 4.0 to about 5.0 and preferably at a pH of about4.5. The pH of the catholyte in the cathode compartments of 'up to about20 amperes per square foot.

the cells employing soluble anodes should be maintained within a rangeof about pH 4.0 to about pH 5.0. The anolyte in the cells havininsoluble anodes should be maintained at about pH 1.25 to about pH 1.5and preferably at about pH 1.4 and the pH of the catholyte of the cellsemploying insoluble anodes should be about 4.0 to 5.0 and preferablyabout pH 4.5. The precipitation of the iron, arsenic and lead withoutsubstantial precipitation of the cobalt is carried out at a temperatureof about F. to about F. and a pH of about 4.0 to about 4.5, andpreferably at a temperature of about 135 F. and a pH of about 4.2. Theremoval of iron, arsenic and lead together with cobalt is carried out ata temperature of about 130 F. to about 135 F. and preferably at about135 F. and a pH of about .0 to about 5.0 and preferably at about pH 4.5.The removal of copper by cementation is carried out at a temperature ofabout 130 F. to about 135 F. and preferably at about 135 F. while the pHis allowed to rise from about 4.2 to about 5.4.

When the cobalt present has not been removed simultaneously with theiron, lead and arsenic, it is preferred to carry out the precipitationof the cobalt at a pH of about 4.0 to about 5.0 and a temperature ofabout 135 F. although satisfactory results can be obtained employing apH of about 4.0 to about 5.0 and a temperature of about 120 F. to about180 F.

In the treatment of primary iron slimes containing cobalt, the pH duringthe reduction of the oxidized slimes to the reduced condition should beallowed to change from pH 6.5 to pH 4.5 by the action of sulfur dioxide.The pH is then reduced to 2.0 by sulfuric acid additions with thetemperature of the reaction maintained within the range of 80 F. toabout F. and preferably at about 120 F. The reoxidation of the reducedions of the primary iron slimes should be carried out within a pH rangeof about 2.0 to about 4.5 and preferably finishing off at about pH 4.5and at a temperature of about F. to about F. and preferably at about 180F. The removal of copper by cementation from the primary iron slimessolution should be carried out at a temperature of about 120 F. to about160 F. and preferably at about 130 F. and within the pH range of about.4.0 to about 5.5 and preferably at about 5. It is preferred to maintaina pH of about 2.3 and a temperature of about 100 F. in precipitating thecobalt from the solution derived from the secondary iron slimes.However, this precipitation may be carried out within the range of aboutpH 1.8 to about pH 2.5 and at a temperature of about 80 F. to about 130F. The electro-deposition of the nickel from the purified electrolyte iscarried out at current densities of It will be noted that these currentdensities are appreciably greater than the current densities generallyemployed in electro-refining nickel from allsulfate electrolytes. Inthis connection it is to be noted particularly that in contrast with thetendency of the electro-nickel to form large berries when currentdensities in excess of 12 amperes per square foot are employed with anall sulfate ion electrolyte, electro-nickel produced in thesulfate-chloride electrolyte does not tend to produce large berries ateven higher current densities for relatively long periods. Consequently,much higher current densities may be employed without encountering thedifficulty arising from the tendency for electro-nickel produced inallsulfate ion electrolytes to produce large berries coarser grained asis recognized by comparison of Figs. 9 and 10. From the standpoint ofpurity, the sulfate-chloride electro-nickel is superior to theall-sulfate ion electro-nickel. For comparison, the following analysisof electro-nickel produced in the all-sulfate electrolyte as compared tothe analysis of electro-nickel produced in the sulfate-ion chlorideelectrolyte in accordance with the process described hereinbefore isprovided:

All-sulfate Sulfate-chloride electrolyte,

per cent Constituents Although the present invention has been describedin conjunction with certain preferred embodiments thereof, those skilledin the art will readily recognize that variations and modifications canbe made. Such variations and modiflcations are to be considered withinthe purview of the specification and the scope of the appended claims.

I claim:

1. A process for electro-refining nickel in an electrolytic cell havingan anode compartment and a cathode compartment separated by a perviousdiaphragm which comprises anodically corroding impure nickel in saidanode compartment with an aqueous solution having sulfate ions andchloride ions as the principal anions and containing about 27 grams toabout 30 grams per liter of chloride ions, and about 71 to about 120grams of sulfate ion per liter while maintaining a pH of about 4.0 toabout 5.0 to thereby obtain an impure anolyte containing iron, copper,cobalt, arsenic and lead in the reduced state, said copper being presentin an amount equal to about 3.0 to about 4.5 times the amount of iron,continuously removing said impure anolyte from said anode compartment,passing air through said impure anolyte to oxidize said copper to thecuprie state, the cupric copper reacting with said iron in the reducedstate to oxidize substantially all of said iron to the ferric statewhereby said iron is hydrolyzed and precipitated without substantialchange in said pH of about 4.0 to about 5.0, treating said impureanolyte with suflicient chlorine gas to oxidize and precipitate arsenicand lead, separating said precipitates of iron, arsenic and lead fromsaid impure anolyte to obtain a partially purified anolyte, removingcopper from said partially purified anolyte by treatment with nickelpowder, separating said nickel powder from said impure anolyte to obtainpartially purified electrolyte, passing additional quantities of chlo-75 rine gas through said partially purified electrolyte while addingsufllcient nickel carbonate to maintain a pH of about 4.0 to about 5.0whereby said cobalt is oxidized and precipitated, separatin said cobaltprecipitate from said partially purified electrolyte to obtain purifiedelectrolyte, introducing said purified electrolyte into said cathodecompartment, and maintaining a sumcient hydrostatic head in said cathodecompartment to substantially prevent the flow of anions from said anodecompartment to said cathode compartment.

2. 'I'heprocess as set forth and described in claim 1 in which thecopper is precipitated at a pH of about 4.0 to about 5.5.

3. The process as set forth and described in claim 1 wherein theelectro-deposition or nickel 01' high purity is carried out at currentdensities of about 12 to 20 amperes per square foot.

4. A process for electro-reiining nickel which comprises establishing anaqueous solution having a pH of about 4 to about 5 containing about 40to about 60 grams of nickel per liter, about 20 to about 30 grams ofsodium per liter, about 27 to about 30 grams of chlorin per liter, about71 to about grams of sulfate ion per liter, about 15 to about 25 gramsof boric acid per liter, not more than 0.01 gram of cobalt per liter,not more than about 0.0001 gram of iron per liter, not more than about0.0005 gram of copper per liter, not more than about 0.0001 gram ofarsenic per liter, and not more than about 0.0001 gram of lead perliter, introducing said electrolyte into the cathode compartment of anelectrodepositing cell, said anode compartment being separated from saidcathode compartment by a porous diaphragm, electro-depositing nickel ata cathode in said cathode compartment, forcing a portion of saidcatholyte through said porous diaphragm into said anode compartmentunder sufficient pressure to substantially prevent copper ions, cobaltions and ions of other impurities, passing through said diaphragm intosaid cathode compartment, anodically corroding an impure nickel anodecontaining copper, iron, cobalt, arsenic and lead, as well as nickel insaid electrolyte forced into said anode compartment thereby obtaining aregenerated electrolyte containing increased amounts of nickel andprohibitive amounts of the impurities cobalt, copper, iron, arsenic andlead in the reduced state, said copper being present in an amount equalto about 3.0 to about 4.5 times the amount of iron, said regeneratedelectrolyte having a pH of about 4 to about 5, passing oxygen throughsaid regenerated electrolyte to oxidize said copper to the cupric state,the cupric copper reacting on the said iron in the reduced state tooxidize substantially all of said iron to the ferric state whilstmaintaining o the'aforesaid pH, passing chlorine into said regeneratedelectrolyte to oxidize said arsenic and lead, allowing suflicient timefor the hydrolysis of saidoxidized iron salts to obtain a precipitatecontaining iron, arsenic and lead, separating said precipitate of iron,arsenic and lead from said regenerated electrolyte to obtain a partiallypurified electrolyte, adding metallic nickel to said partially purifiedelectrolyte to precipitate copper, separating said precipitated copperfrom said partially purified electrolyte to obtain a further purifiedelectrolyte substantially devoid of iron, copper, arsenic and leadimpurities and containing nickel and cobalt, precipitating said cobaltby introducing chlorine and nickel carbonate into said further purifiedelectrolyte, separating said precipitated cobalt from said furtherpurified electrolyte to obtain a purified electrolyte containing about40 to about 60 grams of nickel per liter, about 20 to about 30 grams ofsodium per liter, about 2'7 to about 30 grams of chlorine per liter,about 71 to about 120 grams of sulfate ion per liter, about to about 25grams of boric acid perliter, not more than 0.01 gram of cobalt perliter, not more than about 0.0001 gram of iron per liter, not more thanabout 0.0005 gram of copper per liter, not more than about 0.0001 gramof arsenic per liter, and not more than about 0.0001 gram of lead perliter, and introducing said purified electrolyte into the cathodecompartment of an electro-depositing cell.

5. A process for electro-refining nickel in an electrolytic cellhavingflan anode compartment and a cathode compartment separated by apervious diaphragm which comprises anodically corrodingimpure nickel insaid anode compartment with an aqueous solution comprising essentiallyabout 27 to about 30 grams of chloride ion per liter, about 71 to about120 grams of sulfate ion per liter, about to about 30 grams of sodiumion per liter, and about 15 to about grams of boric acid per liter whilemaintaining a pH of about 4.0 to about 5.0 to thereby obtain an impureanolyte containing about 40 to about 60 grams per liter of nickel, about0.25 to about 0.45 gram per liter of copper, about 0.12 to about 0.15gram per liter of cobalt, about 0.07 to about 0.10 gram per liter ofiron, about 0.0002 to about 0.0004 gram per liter of lead and about0.004 to about 0.006 gram per liter of arsenic in the reduced state,continuously removing said impure anolyte from said anode compartment,passing air through said impure anolyte to oxidize said copper to thecupric state, the cupric copper reacting with said iron in the reducedstate to oxidize substantially all of said iron to the ferric statewhereby said iron is hydrolyzed and precipitated without substantialchange in said pH of about 4.0 to about 5.0. treating said impureanolyte with sufilcient chlorine gas to oxidize and precipitate arsenicand lead, separating said precipitates of iron, arsenic and lead fromsaid impure anolyte to obtain a partially purified anolyte. removingcopper from said partially purified anolyte by treatment with nickelpowder, separating said nicke1 powder from said impure anolyte to obtainpartially purified electrolyte. passing additional quantities ofchlorine gas through said partially purified electrolyte while addingsufficient nickel carbonate to maintain a pH of about 4.0 to about 5.0whereby said cobalt is oxidized and precipitated, separating said cobaltprecipitate from said partially purified electrolyte to obtain purifiedelectrolyte, introducing said purified electrolyte into said cathodecompartment, maintaining a sufiicient hydrostatic head in said cathodecompartment to substantially prevent the flow of anions from said anodecompartment to said cathode compartment, and depositing nickel of highpurity.

6. A process for electro-refining nickel in an electrolytic cell havingan anode compartment and a cathode compartment separated by a perviousdiaphragm which comprises anodically corroding impure nickel. in saidanode compartment with an aqueous solution having sulfate ions andchloride ions as the principal anions and containing about 27 grams toabout 30 grams per liter of chloride ions and about 71 to about 120grams of sulfate ion per liter while maintainin a pH- of about 4.0 toabout 5.0 to thereby obtain an impure anolyte containing iron, copper,cobalt, arsenic and lead in the reduced state, said copper being presentin an amount equal to about 3.0 to about 4.5 times the amount of iron,removing said impure anolyte from said anode compartment, passing arelatively weak oxidizing agent comprising oxygen-containing gasesthrough said impure anolyte to oxidize said copper to the cupric state,the cupric copper reacting with said iron in the reduced state tooxidize substantially all of said iron to the ferric state whereby saidiron is hydrolyzed and precipitated without substantial change in saidpH of about 4 to about 5. oxidizing said reduced arsenic and lead ofsaid impure anolyte to precipitate arsenic and lead, separating saidprecipitates of iron, arsenic and lead from said impure anolyte toobtain a partially purified anolyte, removing copper from said partiallypurified anolyte by treatment with nickel powder, separating said nickelpowder from said impure anolyte to obtain partially purifiedelectrolyte, adding additional quantities of a relatively strongoxidizing agent to said partially purified electrolyte together withsuflicient alkali to maintain a pH of about 4.0 to about 5.0 wherebysaid cobalt is oxidized and precipitated, separating said cobaltprecipitate from said partially purified electrolyte to obtain purifiedelectrolyte, introducing said purified electrolyte into said cathodecompartment, and maintaining a sufilcient hydrostatic head in saidcathode compartment to substantially prevent the flow of anions fromsaid anode compartment to said cathode compartment.

7. A process for electro-refining nicke1 in an electrolytic cell havingan anode compartment and a cathode compartment separated by a perviousdiaphragm which comprises anodically corroding impure nickel in saidanode compartment with an aqueous solution comprising essentially about2'7 to about 30 grams of chloride ion per liter, about '71 to about 120grams of sulfate ion per liter, about 20 to about 30 grams of sodium ionper liter, and about 15 to about 25 rams of boric acid per liter whilemaintaining a pH of about 4.0 to about 5.0 to thereby obtain an impureanolyte containing about 40 to about 60 grams per liter of nickel, about0.25 to about 0.45 gram per liter of copper, about 0.12 to about 0.15gram per liter of cobalt, about 0.07 to about 0.10 gram per liter ofiron, about 0.0002 to about 0.0004 gram per liter of lead and about0.004 to about 0.006 gram per liter of arsenic in the reduced state,continuously removing said impure anolyte from said anode compartment,passing air through said impure anolyte to oxidize said copper to thecupric state, the cupric copper reacting with said iron in the reducedstate to oxidize substantially all of said iron to the ferric statewhereby said iron is hydrolyzed and precipitated without substantialchange in said pH of about 4.0 to about 5.0, treating said impureanolyte with to obtain a purified electrolyte, adjusting'the pH of thepurified electrolyte to about 4.0 to about 5.0 by addition of'acidthereto to obtain a catholyte, introducing said catholyte into saidcathode compartment, and maintaining a sufiicient hydrostatic head insaid cathode compartment to substantially prevent the flow of anionsfrom said anode compartment to said cathode compartment.

8. A process for electro-reflning nickel in an electrolytic cell havingan anode compartment and a cathode compartment separated by a perviousdiaphragm which comprises anodically corroding impure nickel in saidanode compartment with an aqueous solution having sulfate ions, chlorideions and borate ions as the principal anions and containing about 27grams to about 30 grams per liter of chloride ions and about 71 to about120 grams of sulfate ion per liter while maintaining a pH of about 4.0to about 5.0 to thereby obtain an impure anolyte containing iron,copper, cobalt, arsenic and lead in the reduced state, said copper beingpresent in an amount equal to about 3.0 to about 4.5 times the amount ofiron, continuously removing said impure anolyte from said anodecompartment, passing air through said impure anolyte to oxidize saidcopper to the cupric state, the cupric copper reacting with said iron inthe reduced state to oxidize substantially all of said iron to theferric state whereby said iron is hydrolyzed and precipitated withoutsubstantial change in said pH of about 4.0 to'about 5.0, treating saidimpure anolyte with sufiicient chlorine gas to oxidize and precipitatearsenic, lead and cobalt while adding enough nickel carbonate tomaintain a pH of about 4.0 to about. 5.0, separating said precipitatesof iron, arsenic, lead and cobalt from said impure anolyte to obtain apartially purified anolyte, removing copper from said partially purifiedanolyte by successive treatments with nickel powder of progressivelyincreasing purity, separating said nickel powder from said partiallypurified anolyte to obtain a purified electrolyte, adjusting the pH ofsaid purified electrolyte to about 4.0 to about 5.0 by addition of acidthereto to obtain a catholyte, introducing said catholyte into saidcathode compartment, and maintaining a sufficient hydrostatic head insaid cathode compartment to substantially prevent the flow of anionsfrom said anode compartment to said cathode compartment.

9. In a process for continuously purifying an impure nickel electrolytecomprising an aqueous solution having sulfate ions and chloride ions asthe principal anions and containing about 27 to about 30 grams per literof chloride ions and about '71 to 120 grams of sulfate ion per litertogether with nickel. iron, copper, cobalt, arsenic and lead in thereduced state, said copper being present in an amount equal to about 3.0to about 4.5 times the amount of iron, the improvement which consists inremoving iron in said impure electrolyte by passing air through saidimpure electrolyte to oxidize said reduced copper of the impureelectrolyte to the cupric state, the cupric copper reacting with saidiron in the reduced state to oxidize substantially all of said iron tothe ferric state whereby said iron is hydrolyzed and precipitated withina pH range of about 4.0 to about 5.0 and filtering the solution toremove said iron precipitate.

10. A process for electro-refining nickel in an electrolytic cell havingan anode compartment and a cathode compartment separated by a perviousdiaphragm which comprises anodically corrodingimpure nickel in saidanode compartment with an aqueous solution having sulfate ions andchloride ions as the principal anions and containing about 27 grams toabout 30 grams per liter of chloride ions and about 71 to about gramsper liter of sulfate ions while maintaining a pH of about 4.0 to about5.0 to thereby obtain an impure anolyte containing iron, copper, cobalt,arsenic and lead in the reduced state, said copper being present in anamount equal to about 3.0 to about 4.5 times the amount of iron,removing said impure anolyte from said anode compartment, passing airthrough said impure anolyte to oxidize said copper to the cupric state,the cupric copper reacting with said iron in the reduced state tooxidize substantially all of said iron to the ferric state whereby saidiron is hydrolyzed and precipitated without substantial change in saidpH of about 4.0 to 5.0, oxidizing said reduced arsenic, lead and cobaltof said impure. anolyte to precipitate arsenic, lead and cobalt,separating said precipitates of iron, arsenic, 1ead and cobalt from saidimpure anolyte to obtain a partially purified anolyte, removing copperfrom said partially purified anolyte by treatment with nickel powder,separating said nickel powder from said partially purified anolyte toobtain a purified electrolyte, introducing said purified electrolyteinto said cathode compartment and maintaining a sufflcient hydrostatichead in said cathode compartment to substantially prevent the flow ofanions from said anode compartment to said cathode compartment.

11. A process for electro-refining nickel in an electrolytic cell havingan anode compartment and a cathode compartment separated by a perviousdiaphragm which comprises anodically corroding impure nickel in saidanode compartment with an aqueous solution having sulfate ions andchloride ions as the principal anions and containing about 2'7 to 30grams per liter of chloride ions and about '71 to 120 grams per liter ofsulfate ion, while maintaining a pH of about 4.0 to about 5.0 to therebyobtain an impure anolyte containing iron, copper, cobalt, arsenic andlead as impurities, said copper being present in an amount equal toabout 3.0 to 4.5 times the amount of iron, removing said impure anolytefrom said anode compartment, passing air through said impure anolyte tooxidize aid copper to the cupric state, the cupric copper reacting withsaid iron to oxidize substantially all of said iron to the ferric statewhereby said iron is hydrolyzed and precipitated without substantialchange in said pH of about 4.0 to 5.0, oxidizing said arsenic and leadof the impur anolyte to precipitate arsenic and lead, removing copperfrom said impure anolyte by treatment with nickel powder, introducingthe thus-purified electrolyte into said cathode compartment, andmaintaining a sufficient hydrostatic head in said cathode compartment tosubstantially prevent the flow of anions from said anode compartment tosaid cathode compartment.

12. A process for electro-refining nickel in an .electrolytic cellhaving an anode compartment and a cathode compartment separated by apervious diaphragm which comprises anodically corroding impure nickel insaid anode compartment with an aqueous solution containing about 2'7

